Electric power conversion device and control circuit determining occurrence of an abnormality state

Abstract

An electric power conversion device has a transformer, a DC-AC conversion circuit, an AC-DC conversion circuit and a control circuit. The control circuit calculates an input current instruction value (Iref) based on a difference value (ΔV) between an output voltage (Vout) of the AC-DC conversion circuit and an output voltage instruction value (Vref). A comparator compares an input current (Iin) of the DC-AC conversion circuit with the value (Iref). The DC-AC conversion circuit is controlled by the comparison result of the comparator. The control circuit correctly determines an occurrence of an abnormality state of the electric power conversion device based on the operation state of the comparator, the difference value (ΔV) between the output voltage (Vout) of the AC-DC conversion circuit and the output voltage instruction value (Vref), and the input voltage (Vin) of the DC-AC conversion circuit without using any output current of the AC-DC conversion circuit.

What is claimed is: 
     
       1. An electric power conversion device comprising:
 a transformer comprising a primary winding and secondary windings; 
 a direct current-alternating current conversion circuit connected to the primary winding, configured to receive an input current, convert the input current to an alternating current, and supply the alternating current to the primary winding of the transformer; 
 an alternating current-direct current conversion circuit connected to the secondary windings, configured to receive an alternating current supplied from the secondary windings, convert the alternating current to a direct current, and output the direct current; and 
 a control circuit comprising a comparator operating under a current mode control and an abnormality state judgment section; 
 the control circuit being configured to calculate an input current instruction value on a basis of a difference between an output voltage of the alternating current-direct current conversion circuit and an output voltage instruction value, the comparator being configured to compare the input current with the input current instruction value, and the control circuit configured to control operation of the direct current-alternating current conversion circuit on a basis of a comparison result of the comparator, and the abnormality state judgment section determines that the electric power conversion device operates under a normal mode when the comparator operating under the current mode control outputs an output signal which indicates that the input current of the direct current-alternating current conversion circuit is not less than the input current instruction value, and determines an occurrence of an abnormality state in the electric power conversion device when: 
 (a) the comparator operating under the current mode control outputs the output signal which indicates that the input current of the direct current-alternating current conversion circuit is less than the input current instruction value, 
 (b) the difference between the output voltage of the alternating current-direct current conversion circuit and the output voltage instruction value is more than a difference judgment threshold value, 
 wherein the difference judgment threshold value is set in advance to a maximum value of a difference between the output voltage instruction value and the output voltage of the alternating current-direct current conversion circuit, the output voltage is an allowable value when the electric power conversion device works correctly, and 
 (c) an input voltage of the direct current-alternating current conversion circuit is more than an input voltage judgment threshold value, 
 wherein the input voltage judgment threshold value is set in advance to a minimum value which is necessary for adjusting the output voltage of the alternating current-direct current conversion circuit to the output voltage instruction value. 
 
     
     
       2. The electric power conversion device according to  claim 1 , wherein the abnormality state judgment section judges the occurrence of the abnormality state of the electric power conversion device when the comparator outputs the output signal having a level other than a predetermined level, and the difference between the output voltage of the alternating current-direct current conversion circuit and the output voltage instruction value is more than the difference judgment threshold value. 
     
     
       3. The electric power conversion device according to  claim 2 , wherein the abnormality state judgment section determines no occurrence of the abnormality state of the electric power conversion device when the input voltage of the direct current-alternating current conversion circuit is not more than the input voltage judgment threshold value. 
     
     
       4. The electric power conversion device according to  claim 3 , wherein the abnormality state judgment section uses the input voltage judgment threshold value which is a minimum value necessary for controlling that the output voltage of the alternating current-direct current conversion circuit becomes equal to the output voltage instruction value. 
     
     
       5. The electric power conversion device according to  claim 1 , wherein the abnormality state judgment section determines no occurrence of the abnormality state of the electric power conversion device when the input voltage of the direct current-alternating current conversion circuit is not more than the input voltage judgment threshold value. 
     
     
       6. The electric power conversion device according to  claim 5 , wherein the abnormality state judgment section uses the input voltage judgment threshold value which is a minimum value necessary for controlling that the output voltage of the alternating current-direct current conversion circuit becomes equal to the output voltage instruction value.